In a buffer solution, if [A−] = [HA], which of the following must be true?

Question

BlackTom AI · Accepted Answer

When evaluating a buffer consisting of a weak acid HA and its conjugate base A−, the Henderson-Hasselbalch equation is the guiding principle: pH = pKa + log([A−]/[HA]). Option 1: pH = pKa. If [A−] equals [HA], then the ratio [A−]/[HA] equals 1, and log(1) = 0, so pH = pKa. This is exactly what the equation predicts for equal concentrations of acid and conjugate base. Option 2: pH > pKa. This would require [A−]/[HA] > 1 (more base than acid). Since the condition given is [A−] = [HA], this ratio is 1, not greater, so pH cannot exceed pKa under these circumstances. Option 3: pH < 7. While some buffers have pH below 7, the equality [A−] = [HA] only fixes the relation between pH and pKa, not the absolute acid strength or the solution’s ion product. The pH could be above or below 7 depending on pKa, so this statement is not compelled by the given condition. Option 4: pH > 7. Similar to Option 3, this would depend on the actual pKa value and the system’s context. The equal concentrations do not guarantee a basic (pH > 7) buffer; they only fix pH relative to pKa. Option 5: pH < pKa. This would imply [A−]/[HA] < 1. But the given condition is [A−] = [HA], which yields a ratio of 1, not less than 1, so this statement is inconsistent with the Henderson-Hasselbalch relation here. In summary, the equality of the buffer components directly leads to pH equaling pKa via the Henderson-Hasselbalch equation, while all other statements are not implied by the given condition.

In a buffer solution, if [A−] = [HA], which of the following must be true?单项选择题

类似问题

At which ONE of the following pH values would lignocaine hydrochloride (weak base; pKa = 7.9; a local anaesthetic and antiarrhythmic drug) have the slowest dissolution rate?

Question at position 21 What is the pH of a 3.0 M solution of piperidine, C5H10NH? Kb for C5H10NH is 1.3 × 10–3. 5.32 1.20 8.68 12.80

What is the pH of a 0.47 M ammonia solution given Ka for ammonium ion is 5.56 x 10–10?

Find the percent ionization of a 0.337 M HF solution. The Ka for HF is 3.5 × 10-4.

Which of the following statements correctly explains the dissociation of ethanoic acid in water?

Which of the following statements correctly explains the dissociation of ethanoic acid in water?

In which direction does the following equilibrium lie?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单